Drive coupling

ABSTRACT

A drive coupling  10  has an outer plate  12  and an inner plate  14 . Inner plate  14  is positioned within the inner periphery  16  of outer plate  12 . The inner plate  14  includes a plurality of outwardly extending projections  18 . The inner periphery  22  of outer plate  12  includes a plurality of recesses  24.  The drive coupling  10  further comprises a plurality of compression springs  28  arranged between respective projections  18  of inner plate  14  and the respective side wall of the recess  24  of outer plate  12 . A first retaining plate  42  is positioned by passing it over shaft  32 . A spacer ring  48  is positioned such that it abuts one side of the inner plate  14 . A second retaining plate  50  is located on the other of the inner and outer plates. Bolts  56  are used to hold the retaining plates  42  and  50  together. The drive coupling  10  is designed to carry the entire rated torque requirement of the unit on the compression springs, thus providing a continual cushioning action to the drive line whilst allowing a maximum angular movement if an obstruction is encountered.

BACKGROUND TO THE INVENTION

Drive couplings are used in a wide variety of applications. Some examples of drive couplings include chain couplings, disc couplings, doughnut couplings, universal joints or clutches. Drive couplings are typically used to transmit drive from one shaft to another shaft. The shafts may be formed with the drive coupling or they may be connectable to the drive coupling.

In some applications, the equipment being driven by a drive arrangement may be susceptible to sudden shock loads. For example, large multi head grass and scrub cutting machines (termed rotary cutters or slashers) utilise heavy (16 mm to 19 mm thick) cutting blades. To achieve overlap between cutters, the gear boxes which are connected in series by power take off drive shafts are timed so that the blades intersect.

These machines are prone to serious gear box and drive shaft failure. For example, when one individual cutter strikes an obstruction, cumulative forces from the tractor power source, combined with the fly wheel effect (inertia) from all other gear boxes and cutting heads on the machine are transmitted to the individual gear box and shaft coupling involved in the incident.

Standard friction disc type safety clutches cannot be used on these machines, as the cutting blades can only be paused for a few degrees of rotation before contact occurs with adjacent cutting blades.

The most common method of coupling these gear boxes is via chain couplings, disc couplings, doughnut couplings or universal joints. None of these devices provide any predetermined rotational shock relief to transmissions.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a drive coupling that overcomes or at least ameliorates one or more of the abovementioned disadvantages.

In a first aspect, the present invention provides a drive coupling comprising

-   -   an inner plate having one or more outwardly extending         projections,     -   an outer plate having one or more inner peripheral recesses,         each of the one or more inner peripheral recesses having two         inwardly extending wall portions,     -   and one or more coil springs     -   each of the one or more outwardly extending projections of the         inner plate being positioned within an associated inner         peripheral recess of the outer plate, with a coil spring being         located between one face of each of the one or more outwardly         extending projections of the inner plate and one of the inwardly         extending wall portions of the associated inner peripheral         recesses of the outer plate, there being an absence of any coil         spring between another face of each of the projections on the         inner plate and the other inwardly extending wall portion of the         associated inner peripheral recess on the outer plate,     -   wherein rotation of one of the inner plate and the outer plate         causes a reaction force in the at least one coil spring, said         reaction force being transmitted to the other of the inner plate         and the outer plate to thereby cause rotation of the other         plate.         In a second aspect, the present invention provides a drive         coupling comprising     -   an inner plate having one or more outwardly extending         projections,     -   an outer plate having one or more inner peripheral recesses,         with at least one inner peripheral recesses having two inwardly         extending wall portions,     -   and one or more coil springs     -   at least one of the outwardly extending projections of the inner         plate being positioned within an associated inner peripheral         recess of the outer plate, with a coil spring being located         between one face of the outwardly extending projections of the         inner plate and one of the inwardly extending wall portions of         the associated inner peripheral recesses of the outer plate,     -   wherein the one or more coil springs bias the inner plate to a         first position relative to the outer plate when no drive force         is applied to the drive coupling and wherein the inner plate can         move in only one direction from the first position relative to         the outer plate, and     -   wherein rotation of one of the inner plate and the outer plate         causes a reaction force in the at least one coil spring, said         reaction force being transmitted to the other of the inner plate         and the outer plate to thereby cause rotation of the other         plate.

Preferably, during normal use of the drive coupling, the at least one coil spring maintains separation between the inner plate and the outer plate. Suitably, the separation between the inner plate and the outer plate is maintained in a circumferential direction.

The inner plate and the outer plate are preferably in substantial alignment in a longitudinal direction.

The at least one coil spring may be arranged such that it is positioned close to an outer circumference of the outer plate. This minimises torque loadings on the springs.

The drive coupling may further comprise a first retaining plate positioned on one side of the inner and outer plates, a second retaining plate positioned on the other side of the inner and outer plates and connecting means to connect the retaining plates together to thereby maintain the inner and outer plates therebetween.

Preferably, the retaining plates are connected to either the inner plate or the outer plate. More preferably, the retaining plates are connected to the outer plate.

The connecting means for connecting the retaining plates may suitably be bolts. Where the retaining plates are connected to one of the inner or outer plates, that one of the inner or outer plates is suitably provided with apertures for receiving the bolts. The connection means may suitably be large diameter bolts to allow the rapid replacement of internal parts.

The at least one coil spring suitably comprises at least one compression spring, more preferably a plurality of compression springs. However, it will be understood that the present invention should not be considered to be restricted solely to using compression springs as the present invention could also function if tension springs were used.

In one embodiment of the present invention, the inner plate has a plurality of outwardly extending projections and the outer plate has a plurality of inner peripheral recesses, the projections of the inner plate extending into respective recesses of the outer plate, and the at least one coil spring comprises a plurality of coil springs, each positioned between a respective projection of the inner plate and a wall of the corresponding recess of the outer plate.

The projections of the inner plate may extend in a generally radial direction. The recesses in the inner periphery of the outer plate may be defined by inwardly extending portions of the inner peripheral wall of the outer plate.

In embodiments where the at least one coil spring comprises a plurality of compression springs, the drive coupling may further comprise positioning means on one of the inner plate or outer plate to position the compression springs. Preferably, the positioning means are formed on or connected to the outer plate.

The positioning means may comprise spring guide projections extending from one wall of each recess of the outer plate. The spring guide projections may be sized such that the compression springs fit over the projections.

The drive coupling of the present invention may further comprise a shaft connected to or formed with one of the inner or outer plates. Preferably, the inner plate has a first shaft formed therewith or attached thereto.

The other plate may also include a shaft formed therewith or connected thereto. In embodiments where retaining means are used to maintain relative axial positioning between the inner plate and the outer plate, one of the retaining plates may include a shaft connecting means for connecting a shaft thereto, or it may have a shaft attached thereto.

In embodiments where a positively located (or non-floating) drive shaft is required, the coupling may include a male member extending from a solid male shaft and extending into a locating bush housed in the flange end of the retaining plate. Suitably, the male member exrtends through the inner plate and through an opening in the outer plate into the bush.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of a drive coupling in accordance with an embodiment of the present invention. In FIG. 1, the retaining plates have been removed for clarity; and

FIG. 2 shows a cross-sectional side view of a drive coupling in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated that the drawings attached to the specification have been provided for the purposes of illustrating preferred embodiments of the present invention. Thus, the present invention shall not be considered to be limited to the embodiments shown in the attached drawings.

The drive coupling 10 shown in FIGS. 1 and 2 comprises an outer plate 12 and an inner plate 14. As best shown in FIG. 1, inner plate 14 is positioned within the inner periphery 16 of outer plate 12. As best shown in FIG. 2, outer plate 12 and inner plate 14 are in substantial alignment in a longitudinal direction. If the outer plate 12 and inner plate 14 are of differing thicknesses, the inner plate and outer plate may be aligned such that their transverse centre lines are in alignment, or such that one side of each plate is in alignment.

The inner plate 14 includes a plurality of outwardly extending projections 18. For the sake of clarity, only some of these projections 18 are numbered in FIG. 1. The projections 18 extend in a generally radially direction. The outer periphery of inner plate 14 includes regions of relatively smaller diameter 20 located between adjacent outwardly extending projections 18.

The inner periphery 22 of outer plate 12 includes a plurality of recesses 24. For the sake of clarity, only some of the recesses 24 have been numbered in FIG. 1. The recesses 24 are bounded by inwardly extending projections 26 on the outer plate 12.

As can be seen from FIG. 1, each projection 18 of the inner plate 14 is positioned such that it is within a corresponding recess 24 defined by the outer plate 12.

The drive coupling 10 further comprises a plurality of compression springs 28. Compression springs 28 are in the form of heavy duty coil springs. For the sake of clarity, only some of the compression springs 28 have been numbered in FIG. 1. As can be seen from FIG. 1, the compression springs 28 are arranged between respective projections 18 of inner plate 14 and the respective side wall of the recess 24 of outer plate 12. To assist in positioning the compression springs 28, the respective walls of recesses 24 are provided with spring guide means 30. For the sake of clarity, only some of spring guide means 30 are numbered in FIG. 1. Spring guide means 30 take the form of a projection extending outwardly from the wall of recess 24, which projection is sized such that the compression spring 28 can be fitted over projection 30.

The drive coupling 10 further includes a shaft 32 that is connected to the inner plate 14. Shaft 32 is suitably connected to inner plate 14 by welding. The shaft 32 has a central cavity 34, which cavity 34 is arranged to receive and hold a splined shaft (not shown). In this manner, a splined drive shaft can be connected to shaft 32. The splined shaft that is received within the cavity 34 of shaft 32 may be telescopically movable inside cavity 34.

In another embodiment, shaft 32 may be in the form of a solid shaft which may be positively inserted located within a bush within retaining plate 50 by means of a spigot extending from the internal end of shaft 32. This is useful in situations where positive, or non-floating, location of the drive is required.

The outer plate 12 further includes a plurality of apertures 36. For the sake of clarity, only some of the apertures 36 have been numbered in FIG. 1. Apertures 36 receive the shanks of bolts that are used to connect the retaining plates to each other. This will be described in greater detail with reference to FIG. 2.

In order to assemble the drive coupling shown in FIG. 1, the compression springs 28 are placed on the spring guide projections 30. The compression springs are then compressed by placing inner plate 14 into position such that projections 18 abut on the ends of springs 28 and thereafter rotating inner plate 14. The inner plate 14 can then fit into place within outer plate 12. Alternately, spring compressors may be used to compress the springs and fit the inner plate 14, but this would involve extra steps during assembly of the drive coupling 10. It will be appreciated that the compression springs are retained in place by the respective parts of the outer peripheral wall of inner plate 14 and the inner peripheral wall of outer plate 12 and the spring guides 30.

In order to maintain the axial positioning of the outer plate 12 and the inner plate 14, an assembly as shown in FIG. 2 may be used. Before explaining the assembly shown in FIG. 2, reference will be made to FIG. 2 to show that the shaft 32 extends through a central aperture in inner plate 14 such that a small portion 38 of shaft 32 extends beyond the other side of inner plate 14. Weld metal 40 is used to connect the inner shaft 32 to the inner plate 14.

The assembly shown in FIG. 2 includes the outer plate 12 and inner plate 14 arranged as shown with reference to FIG. 1. A first retaining plate 42 having a central opening 44 that is large enough to fit over shaft 32 is positioned by passing it over shaft 32 such that it reaches the position shown in FIG. 2. First retaining plate 42 includes a plurality of apertures 46. Apertures 46 are positioned such that they can be brought into alignment with the apertures 36 in the outer plate 12.

Prior to positioning first retaining plate 42 as shown in FIG. 1, a spacer ring 48 is positioned such that it abuts one side of the inner plate 14.

The assembly shown in FIG. 2 further includes a second retaining plate 50 that is located on the other side (to the side on which first retaining plate 42 is positioned) of the inner and outer plates. Second retaining plate 50 includes a plurality of apertures 52. The plurality of apertures 52 are arranged on second retaining plate 50 such that they can be brought into alignment with the apertures 36 of the outer plate 12.

As shown in FIG. 2, an inner surface 54 of second retaining plate comes into contact with the end of small portion 38 of shaft 32 which is attached to inner plate 14.

In order to connect the first and second retaining plates, bolts 56 are inserted through the respective apertures 52, 36 and 46. Spacers 58 are positioned on either side of the outer plate 12 to properly space the first and second retaining plates from the outer plate 12. Nuts 60 are subsequently placed over the threaded ends of bolts 56 and tightened to thereby hold the retaining plates 42 and 50 together. It will be appreciated that the bolts 56 pass through the apertures 36 in the outer plate 12. Furthermore, the spacer ring 48 and the small portion 38 of the shaft 32 are in contact with the respective retaining plates. In this fashion, the retaining plates act to retain the inner plate in position relative to the retaining plates (and relative to the outer plate 12). However, the inner plate 14 is only lightly clamped against the retaining plates 42 and 50, and a degree of rotational movement between the inner plate 14 and the retaining plates is possible.

The second retaining plate 50 forms part of a larger structure 62. Structure 62 includes a half split sleeve 64 that is welded to or formed with the second retaining plate 50. Half split sleeve 64 has a cavity 66 that is able to receive a splined shaft (not shown). Bolt holes 68 are provided so that, after inserting a splined shaft into cavity 66, bolts (not shown) can be used to tighten the half split sleeve 64 to thereby prevent axial removal of the splined shaft from the cavity 66. In this manner, the half split sleeve 64 can be connected to a splined shaft, such as a splined drive shaft of a power take off from a tractor, with the splined shaft being constrained against rotational and axial movement relative to the half split collar 64.

In use of the assembly shown in FIGS. 1 and 2, the drive shaft (not shown) attached to half split sleeve 64 rotates. The direction of rotation is shown by arrow 70 in FIG. 1. Rotation of the drive shaft will, of course, cause rotation of outer plate 12 in the direction shown by arrow 70 in FIG. 1. This causes compression of the compression springs 28. Compression of the compression springs causes a reaction force to be imparted from the compression springs onto the projections 18 of the inner plate 14. When this reaction force equals the resistance to rotation that is felt by the inner plate 14, the inner plate 14 starts to rotate as well. Thus, it can be seen that the drive coupling shown in FIGS. 1 and 2 provides for the continual rated working load of a machine to be transmitted by the compression springs 28. If there are any sudden shocks felt by the machinery being driven by the drive coupling, the sudden shock loads are absorbed by the springs which allow for a predetermined amount of relief rotation of the coupling input shaft.

To assemble drive couplings requiring reverse rotation to that shown in FIG. 1, outer plate 12 and inner plate 14 are inverted during assembly.

The drive coupling shown in the embodiment of the present invention of FIGS. 1 and 2 is designed to carry the entire rated torque requirement of the unit on the compression springs, thus providing a continual cushioning action to the drive line. When a sudden shock load is encountered, the compression springs compress to a predetermined torque value, and a predetermined angular value to provide a maximum angular movement. If the drive coupling is to be used on a multi head grass and scrub cutting machine, this maximum angular movement can be set such that interaction of the output cutting blades is avoided. Using coil springs to carry the normal torque load of the shaft allows a cushioned drive to be obtained whilst also allowing predetermined maximum angular movement in the event that an obstruction is encountered.

The maximum angular movement allowed for by the drive coupling can be explained by reference to FIG. 1. When the drive coupling is undergoing normal use, the springs 28 are compressed to a small degree in response to the resistance to rotation felt by the inner plate 14. If a shock load is felt, the springs 28 can compress to a maximum extent (in which either the coils of the springs come into full contact with each other or the respective ends of spring guides 30 contact respective projections 18). Further rotation of the inner plate relative to the outer plate is thereafter not possible, thereby providing for a maximum amount of angular rotation between the inner and outer plates.

It will be appreciated that the present invention may be subjected to variations and modifications that are not shown. For example, rather than using compression springs, tension springs may be used. If tension springs are used, the tension springs will need to be firmly connected to the walls 26 of outer plate 12 and the projections 18 of inner plate 14. Further, the direction of rotation 70 shown in FIG. 1 will need to be reversed. In this fashion, as the outer plate is rotated (in the opposite direction to the direction 70 shown in FIG. 1), the tension springs will extend slightly until the force imparted by the tension springs equals the resistance to rotation of the inner plate. Although such an arrangement is possible, it is not preferred as it would entail a more complex assembly procedure.

The present invention provides a simple yet rugged drive coupling that enables cushioning of shock loads. Embodiments of the invention utilise circumferentially mounted coil springs to transmit a cushioned torque load to the output shaft while providing overload travel to a predetermined figure. Torque is transmitted to the springs by one piece inner and outer drive plates obviating the need for multi spring holders and pins. The springs are located (externally and internally) by one piece plates eliminating the possibility and danger of spring dislodgement from the rotating coupling. Both male and female output shafts can be incorporated with accommodation for telescopic power takeoff shafts without fear of coupling separation. The drive coupling is able to accept high axial loads by use of the retaining plate arrangement shown in FIG. 2 to prevent the unit from separating under axial loads.

Those skilled in the art will appreciate that the present invention may be subject to variations and modifications other than those specifically described. It is to be understood that the invention encompasses all such variations and modifications that fall within its spirit and scope. 

1. A drive coupling comprising an inner plate having one or more outwardly extending projections, an outer plate having one or more inner peripheral recesses, each of the one or more inner peripheral recesses having two inwardly extending wall portions, and one or more coil springs each of the one or more outwardly extending projections of the inner plate being positioned within an associated inner peripheral recess of the outer plate, with a coil spring being located between one face of each of the one or more outwardly extending projections of the inner plate and one of the inwardly extending wall portions of the associated inner peripheral recesses of the outer plate, there being an absence of any coil spring between another face of each of the projections on the inner plate and the other inwardly extending wall portion of the associated inner peripheral recess on the outer plate, wherein rotation of one of the inner plate and the outer plate causes a reaction force in the at least one coil spring, said reaction force being transmitted to the other of the inner plate and the outer plate to thereby cause rotation of the other plate.
 2. A drive coupling as claimed in claim 1 wherein the inner plate has a plurality of outwardly extending projections and the outer plate has a plurality of inner peripheral recesses, the projections of the inner plate extending into respective recesses of the outer plate, and the one or more coil springs comprise a plurality of coil springs, each positioned between a respective projection of the inner plate and a wall of the corresponding recess of the outer plate.
 3. A drive coupling as claimed in claim 2 wherein the projections of the inner plate extend in a generally radial direction and the recesses in the inner periphery of the outer plate are defined by the inwardly extending wall portions of the inner peripheral wall of the outer plate.
 4. A drive coupling as claimed in any one of the preceding claims wherein the inner plate and the outer plate are in substantial alignment in a longitudinal direction.
 5. A drive coupling as claimed in any one of the preceding claims wherein the one or more coil springs are positioned in a generally circumferential direction.
 6. A drive coupling as claimed in any one of the preceding claims further comprising a first retaining plate positioned on one side of the inner and outer plates, a second retaining plate positioned on the other side of the inner and outer plates and connecting means to connect the retaining plates together to thereby maintain the inner and outer plates therebetween.
 7. A drive coupling as claimed in claim 6 wherein the retaining plates are connected to the outer plate.
 8. A drive coupling as claimed in claim 7 wherein the connecting means for connecting the retaining plates comprise bolts and the outer plate is provided with apertures for receiving the bolts.
 9. A drive coupling as claimed in any one of the preceding claims wherein the one or more coil springs comprise one or more compression springs.
 10. A drive coupling as claimed in claim 9 further comprising positioning means on one of the inner plate or outer plate to position the one or more compression springs.
 11. A drive coupling as claimed in claim 10 wherein the positioning means comprises spring guide projections extending from one wall of each inner peripheral recess of the outer plate.
 12. A drive coupling as claimed in claim 11 wherein the spring guide projections are sized such that the compression springs fit over the projections.
 13. A drive coupling as claimed in any one of the preceding claims further comprising a shaft connected to or formed with one of the inner or outer plates.
 14. A drive coupling as claimed in claim 13 wherein the inner plate has a first shaft formed therewith or attached thereto.
 15. A drive coupling as claimed in claim 13 or claim 14 wherein the outer plate has a shaft formed therewith or connected thereto.
 16. A drive coupling as claimed in claim 6 wherein one of the retaining plates has a shaft connecting means for connecting a shaft thereto, or has a shaft attached thereto.
 17. A drive coupling as claimed in any one of the preceding claims wherein during normal use of the drive coupling, the at least one coil spring maintains separation between the inner plate and the outer plate in a circumferential direction.
 18. A drive coupling comprising an inner plate having one or more outwardly extending projections, an outer plate having one or more inner peripheral recesses, with at least one inner peripheral recesses having two inwardly extending wall portions, and one or more coil springs, at least one of the outwardly extending projections of the inner plate being positioned within an associated inner peripheral recess of the outer plate, with a coil spring being located between one face of the outwardly extending projections of the inner plate and one of the inwardly extending wall portions of the associated inner peripheral recesses of the outer plate, wherein the one or more coil springs bias the inner plate to a first position relative to the outer plate when no drive force is applied to the drive coupling and wherein the inner plate can move in only one direction from the first position relative to the outer plate, and wherein rotation of one of the inner plate and the outer plate causes a reaction force in the at least one coil spring, said reaction force being transmitted to the other of the inner plate and the outer plate to thereby cause rotation of the other plate.
 19. A drive coupling substantially as hereinbefore described with reference to the accompanying drawings. 